Chlorination of aromatic polysocyanates



F TQ 1* AROM H POLYISOCYANATES James iunki hiTazuma; Trenton, as ignor to Food M c ne andJC e ie l fi n, New York,

N.Y., a corporation of Delaware I No'nrawiiig: Files lrp'r.-1 19s1, sea No. 649,621

8 Claims. (or. 260-453 This'invention relates to the chlorination and'bromination' of aromatic: polyisocyanates. I More, particularly, this inventionrelates to the chlorination and bromination of the benzene nucleus of aromatic polyisocyanates.

Aromatic polyisocyan'ates; particularly aromatic diisocyanates having a benzene nucleus, such as m-phenylene diisocyanate, :p-ph'enylcne diisocyanate, 2 ,4- and 2,6- tolylene diisocyanatezandmixtures of these have found considerable applicationnin recentyear's as intermediates in the manufacture'offirigidand= flexible foams; adhesive c ating highi yxal'irasionvresistant rubber substitutes.

'In certain of these applications it'has beenfound advantageous to replace part or all of the aromatic diisocyanate by a halogenated aromatic dii'socyanate; For example; the: halogenated, aromatic. isocyanates are generally more reactive with active-hydrogen compounds, suchv as alcohols;phenols, 'mercaptans, and carboxylic acids, than are the corresponding non-halogenated isocyanates. Furthermore, compositions derived from halogenated aromatic diiso cyanates tend to exhibit enhanced flame resistancegreater stability towards sunlight, and'oth'er desirable'qualitiesi; p f

. It has beensuggested to prepare chlorinated aromatic diis'ocya'na'tes by dissolving. the isofcyanate' iii an inert solvent, such as carbon tetrachloride, chloroform and tetrachloroethane, and thenpass chlorine gas through the diisocyanate solution. Such a system has the following disadvantages, namely, necessity of separating the solvent and reaction product, slow rate of reaction and low volume-productivity.

Furthermore, said solvent system results in the formation of an intermediate carbamyl chloride which must be further reacted to yield the chlorinated isocyanate. I It is an object of this invention to provide an economical process for the preparation of mono and di-chlorinated or brominated aromatic polyisocyanates having a benzene nucleus, wherein the halogen is nuclear substituted.

It is a further object of this invention to provide a process for preparing mono and iii-chlorinated or brominated aromatic polyisocyanates of this invention that avoids the use of a solvent and its attendant disadvantages.

Other objects will appear to those skilled in the art as the description of this invention unfolds.

, Generally stated, this invention provides a process for preparing mono and di-chlorinated or brominated aromatic polyisocyanates, said aromatic polyisocyanates having one or more benzene rings as the nuclear group or groups and the chlorine or bromine being substituted in the benzene ring. It has been discovered that aromatic polyisocyanates having a benzene ring or rings as the nuclear group may be chlorinated or brominated by reacting halogen and a liquefied polyisocyanate.

Thus, contrary to the teachings of the prior art that'it is necessary to employ a solvent to effect chlorination or bromination of aromatic polyisocyanates, it has been found that by directly chlorinating or brominating a r 2,945,875, i ee e-w 19 molten or liquid polyisocyanate; a mixture of mono: and di-chlorinated or- 'd-ib'rominated product obtained in excellent yield.

Examples of the aromatic polyisocyanates which may be chlorinated or brominatedin accordance with this invention are p-phenylene diisocyanate, m-phenylene diisocyanate, 4,4-biphenylen'e diisocyanate, 3,3'-dirnethyl 4,4'- biphenylene diiso cyan'ate, 414"-niethyle'nebisfliherlyl isocyanate), 4,4'-methylene' bis(2 rnethyl plienyl isocyariate), 2,4-tolylene diisocyanate, corresponding triisocyanates and mixtures of these compounds.

Table I is a listing of the melting oints of several of the diisocyanates of this invention.

TABLE I Solidifieationtor Compound Melting Point 53 91 v 21 122 ill eyanate 69 4,4-methylene bis(phenyl isoeyanate)" 37 4,4-methylene bis(2-methylphenyl isocyanate) 31 The chlorination or bromination may be performed at a temperature above the melting point and below the boiling point of theparticular polyisocyanate. A preferred temperature is between 15 0 160: C, v v 7 W Chlorine may be introduced into the reactor by having a conventional gas inlet tube situated belowitl'ie liquid level. Preferably, the. chlorine is introduced. at or near the bottom of-the'reactor.- 'lfhough the'passagethrough the reaction mass of unreatedchlorinegand' by-product HCLfunctionas an agitating force,-- it ispreferabIe to provide agitating means, such as a mechanical stirrer; i

In the case of bromination, liquid, bromine may be added in desired-portions, When-brorninating, it-is preferrd to agitate the liquid p'olyisocyanate by mechanical means.

The halogenation is ordinarily conducted at atmospheric pressure though superatmospheric pressures may be used advantageously in some instances.

Materials of construction that resist corrosion by chlorine, bromine, hydrogen chloride, hydrogen bromide polyisocyanate and chlorinated and brominated polyisocyanate are preferred. Equipment may be fabricated of glass, porcelain, glass-lined steel, stainless steel, or carbon steel.

Depending upon the temperature of the reaction, the polyisocyanate will be more or less dichlorinated. The higher the temperature, the greater will be the amount of dichlorinated product.

For most commercial uses of the chlorinated polyisocyanates, it is not necessary that a separation of the mono and di-chlorinated components be undertaken. However, if need be, the two components may be separated by rectification or recrystallization from a suitable solvent, such as hexane.

Furthermore, the chlorination and distillation steps may be carried out either continuously or batchwise.

Following is set forth examples serving to illustrate this invention.

Example I The apparatus used in this example comprises a 500 ml. 3-neck flask fitted with a thermometer, a mechanical stirrer, a gas inlet tubeextending below the liquid level, and an electrically heated Vigreaux column! The Vigreaux column is maintained at about C. throughout the chlorination. 'The flask is charged with 160.8 (1.0 mol) grams of m-phenylene diisocyanate and warmed to 150 C. Chlorine is passed in at a rate of I 1.5 mols per hour for a period of 4.5 hours. During this Example ll The apparatus used in this example is the same as in Example I. The Yigreaux column being maintained at 100 C. throughout the chlorination. The flask was charged with 161 grams(1'mol) of m-phenylene diiso- 'cyanate and, warmed to 150 C. Chlorine was passed into the liquid diisocyanate at a rate of 1.5 mols per hour for a period of 4.5 .hours. During this period the temperature was maintained between 120-130 C. 'About 1.3ino1s'of chlorine reacted with the diisocyanate. The chlorinated reaction product was vacuum distilled and recovery had of 95% of the reaction mixture boiling between 152 and 175 C. at pressure between 38 to 46 mm. Hg. This product comprised about 70% monochloro and 30% dichloro-1,3-phenylene diisocyanate.

Table II shows physical constants for mono and dichloro m-phenylene diisocyanate.

Iabl e II Boiling Point Meling Analysis Compound 0.)]mm. Roint P rH Cl 0 H Monochloro L 155-56/34 70 18.2 49.4 1. s Dichl0r0-.. V 17677/33 84 30.9 42.0 0.9

- Pursuant to therequirements of the patent statutes, the principle of this invention has been explained and exemplified in'a manner-so that it can be readily pracunderstood that, within the the invention may be practiced by-thoseskilled. inthe scope of the appended claims,

art, and having the benefit of this disclosure, otherwise than as specifically described and exemplified herein.

That which is claimed as patentably novel is:

1. The method of preparing mono and di-nuclear halogenated aromatic diisocyana-tes which comprises reacting a halogen selected from the group consisting of chlorine and bromine with a molten mass of an unsubstituted aromatic diisocyanate selected from the group consisting of phenyl, biphenyl and methylene bisphenyl diisocyanates at a temperature above the melting point and below the boiling point of the diisocyanate, and in the absence of solvent, thereby substituting halogen on the aromatic nucleus of the diisocyan ate to produce said nuclear halogenated diisocyanat'e'.

2. The method of preparing a mixture of monoand di-chlorinated meta-phenylene diisocyanates which comprises reacting chlorine with 'a molten mass of metaphenylene diisocyanate, at a temperature of about 120-- -'160 C., in the absence of solvent, thereby substituting chlorine on the aromatic nucleus of the meta-phenylene diisocyanate to produce said mixture of monoand dichlorinated meta-phenylene diisocyanates.

3. The method of claim 1, wherein the aromatic diisocyanate is a phenylene diisocyanate. '4. Themethod ofclaim 1, wherein the aromatic diisocyanate is a meta-phenylene diisocyanate. 5. The-method of claim 1, wherein the diisocyanate is a biphenyl'diisocyanate. 1 -6. The method of claim 1, wherein is a methylene bisphenyl diisocyanate.

7, The method of claim 1, wherein the chlorine.- a 8. The method-of claim 1, wherein the halogen is the diisocyanate halogen is bromine. I p f f References Cited in the file of this patent Siefken: Justus Liebigs Annalen der Chemie, 1949 (Bande 562),pgs. -91.

Grogginsr Unit Processes in Organic Synthesis, fourth edition, 1952, pgs. 206-207. 

1. THE METHOD OF PREPARING MONO- AND DI-NUCLEAR HALOGENATED AROMATIC DIISOCYANATES WHICH COMPRISES REACTING A HALOGEN SELECTED FROM THE GROUP CONSISTING OF CHLORINE AND BROMINE WITH A MOLTEN MASS OF AN UNSUBSTITUTED AROMATIC DIISOCYANATE SELECTED FROM THE GROUP CONSISTING OF PHENYL, BIPHENYL AND METHYLENE BISPHENYL DIISOCYANATES AT A TEMPERATURE ABOVE THE MELTING POINT AND BELOW THE BOILING POINT OF THE DIISOCYANATE, AND IN THE ABSENCE OF SOLVENT, THEREBY SUBSTITUTING HALOGEN ON THE AROMATIC NUCLEOUS OF THE DIISOCYANATE TO PRODUCE SAID NUCLEAR HALOGENATED DIISOCYANATE. 